The present invention relates to methods and apparatus for treating substrates such as semiconductor wafers with liquids.
In the semiconductor processing art, it is often necessary to treat a semiconductor wafer with a liquid. A typical semiconductor wafer has a flat active surface that must be exposed to liquids such as developers for developing photoresists, electroless plating solutions and electroplating solutions, as well as rinsing liquids that are commonly used to remove other liquids. In many cases, it is important to expose all parts of the active surface to the liquid for the same length of time. For example, to etch a wafer surface uniformly using a chemical etchant, the entire surface should be exposed to the etchant for the same duration. If a wafer is dipped into an etchant bath with the active surface extending vertically, the part of the active surface at the bottom of the wafer will enter the bath first as the wafer is immersed, and will leave the bath last as the wafer is withdrawn from the bath. This part of the active surface will be exposed for a longer time than the part of the active surface near the top of the wafer. Because the wafer must be immersed and withdrawn at a moderate speed to avoid turbulence and bubble entrainment, the difference in exposure time can be considerable. This difference is especially significant where the total exposure time is small as, for example, with a fast-acting etchant. Similar problems arise in treatment with other liquid solutions.
In other wafer processing techniques, the wafer is moved downwardly into the liquid with the active surface in a horizontal orientation and facing downwardly. In theory, the entire surface can enter the liquid at the same time and can leave the liquid at the same time. In practice, however, this approach tends to trap air bubbles at the surface, leading to non-uniform contact. Other liquid contacting methods such as spraying suffer from other drawbacks, including difficulty in assuring uniform contacting conditions for the entire active surface.
The present invention provides apparatus and methods, which alleviate these drawbacks.
One aspect of the invention provides methods of treating a solid substrate such as a semiconductor wafer with one or more liquids. A method according to this aspect of the invention desirably includes the steps of providing a first liquid in a first vessel having an open top and moving the substrate in a feed direction across the vessel so that a surface of the substrate faces downwardly and successive portions of such surface contact the liquid in the vessel as such portions pass across the vessel. The step of providing a first liquid may include the step of continually feeding the first liquid into the vessel so that the first liquid continually overflows the first vessel, most preferably in a slow, steady flow at the minimum rate required to maintain the surface of the first liquid just slightly above the edge of the vessel. The first vessel may be an elongated trough having upstream and downstream edges at the top of the first vessel extending substantially parallel to one another and substantially transverse to the feed direction.
The surface of the substrate preferably moves across the vessel at a substantially constant velocity, so that every portion of the substrate surface is exposed to the liquid for substantially the same length of time. The method may also include the step of providing a second liquid in a second vessel having an open top, said second vessel being offset from said first vessel in said feed direction so that each portion of the substrate passes across the second vessel and contacts the second liquid after contacting the first liquid. More than two vessels may be employed.
A further aspect of the invention provides apparatus for treating a substrate. Apparatus according to this aspect of the invention may include a first vessel having an open top and a first liquid source connected to the first vessel. The first liquid source is constructed and arranged to provide a first liquid in said first vessel so that the first liquid rises above the top of the first vessel. The apparatus also includes a conveyor arranged to convey a substrate over the first vessel in a feed direction so that a surface of the substrate faces downwardly and such surface moves across the first vessel and contacts the first liquid. As discussed above in connection with the method, the apparatus may also include a second vessel and second liquid source.
These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below, taken in conjunction with the accompanying drawings.